Experimental Study: Foam Generation and Propagation in Flow Across a Permeability Contrast

Abstract

Foam is useful as an enhanced oil recovery method to reduce gas mobility and prevent gravity override to improve sweep efficiency. Foam is generated in porous media when exceeding a critical velocity and pressure gradient, that usually occur near to an injection well. There is the uncertainty of foam generation in the low-pressure gradient and velocity further from the injection well. However, foam can be generated at such a permeability change with no minimum pressure gradient or superficial velocity. In field application, permeability contrasts originate from cross-bedding in fluvial sand-channel reservoirs, reservoir layering, and sharp heterogeneity changes over a few centimeters to kilometers of the formation.

This study describes series of experiments with various of gas fractional flows, and injection velocities. The experiments use synthetic sintered glass porous media to create consolidated nature of porous medium with a sharp boundary between low- and high-permeability layers. The experiments are augmented by the medical X-ray computerized tomography (CT) machine, which can be used to generate dynamic images of the core flood.

This study proves that capillary snap-off plays a dominant role in foam generation across a sharp heterogeneity boundary (low to high permeability) regardless of the superficial injection velocity that is applied in the system. In our experiments, as the injection velocity reduced, the magnitude of pressure fluctuations increase. Across the permeability jump, as the injection velocity reduces, the observed pressure gradient during foam generation is also higher. However, foam is difficult to propagate at very low injection velocity, in our case 0.17 ft/day (0.025 ml/min). These conditions observed at sintered glass core with permeability contrast 3.8:1 (0.17 ft/day and 80% of foam quality) and permeability contrast 14:1 (0.17 ft/day and 95% of foam quality). In terms of gas fractional flow, the CT results verify the pressure gradient profile at different gas fractional flow experiments (60%, 80\%, and 95%), foam is indeed generated at the permeability contrast and propagates downstream to the outlet of the core.